This O-ring seals the hydraulic filter housing on the host tractor, preventing fluid bypass around the filter element. It sits between the housing cap and the filter canister, maintaining the pressure differential required for proper filtration. A degraded or pinched O-ring allows unfiltered fluid to reach the hydraulic pump, causing accelerated wear in the valve and actuator circuits. Manufactured by AGCO, the O-ring is molded to match the original seal groove geometry so the housing cap seats correctly and the bypass valve cracks at the intended pressure. Replace the O-ring each time the filter element is changed, and verify the seal surface is clean before installation.